Prostate cancer is the most common cancer, excluding non-melanoma skin cancers, in American men. The American Cancer Society estimates that in the year 2000 approximately 180,400 new cases of prostate cancer were diagnosed in the United States. Prostate cancer is the second leading cause of cancer death in men, exceeded only by lung cancer. Prostate cancer causes about 11 percent of all cancer deaths in men. Furthermore, it is estimated that approximately 5 million men have at this very moment a histological cancer of the prostate, which may or may not ever become clinically evident. The prostate gland is about the size of a walnut and is located anterior to the rectum, adjacent to the bladder and surrounds the proximal part of the urethra. It contains glandular epithelium that produces a portion of the seminal fluid which protects and nourishes sperm cells. Although other cells exist in the prostate, over 99% of prostate cancers develop are adenocarcinomas.
Prostate cancer is a multi-focal disease with clones of androgen-sensitive and androgen-refractory cells (N. Kyprianou and J. Isaacs, Biochem. Biophys. Res. Comm., 165, 73-81, 1989; Kyprianou, N., et al., World J. Urol., 12, 299-303, 1994; M. Tenniswood and H. Michna, Ernst Schering Research Foundation Workshop, 14, Springer-Verlag, Berlin Heidelberg, 1995). The role androgen receptors (AR) may play in prostate cancer is not clear. Although androgen depletion therapy results in regression of the tumor, it returns as an androgen-refractory cancer. Some androgen-refractory tumors express increased levels of androgen receptors, suggesting that continued proliferation of androgen-refractory prostate cells may be influenced by androgens (Linja, M. J., et al., Cancer Res., 61, 3350-3555, 2001). Paradoxically, increased expression of AR may also be responsible for inhibition of growth and may induce apoptosis (Joly-Pharaboz, M. O., et al., J. Steroid Biochem. Mol. Biol., 55, 67-76, 1995; Joly-Pharaboz, M. O., et al., J. Steroid Biochem. Mol. Biol., 73, 237-249, 2000; Dai, J. L., et al., Steroids, 61, 531-539, 1996; Umekita, Y., et al., Proc. Natl. Acad. Sci., USA, 93, 11802-11807, 1996; Zhau, H. Y. E., et al., Proc. Natl., Acad. Sci., USA, 93, 15152-15157, 1996; Heisler L. E., et al., Mol. Cell. Endocr., 126, 59-73, 1997; Shen, R., et al., Endocrinology, 141, 1699-1704, 2000).
Patients diagnosed with a clinically localized or “early-stage” prostate cancer may be treated with surgery, radiation, local ablation, or by non-treatment or “watchful waiting.” The conventional surgery is a radical prostatectomy, which can be performed through a retropubic approach, a perineal approach, or in the case of laparoscopy through a transperitoneal approach. Surgery is usually reserved for locally confined disease and is usually curative. (Catalona W J et al., “Contemporary results of anatomic radical prostatectomy,” CA Cancer J Clin 40: 282, 1999). These procedures are invasive, possess significant side effects (urinary incontinence and impotence), and require hospital stays and time out of work. Definitive surgical treatment to extirpate the early stage cancer often involves some type of radical prostatectomy. Modifications of surgical techniques have been developed to preserve potency in patients undergoing radical prostatectomy. (Walsh, P. C. “Anatomic radical prostatectomy: evolution of the surgical technique”. J Urol, 160:2418-2424, 1998.). Meticulous surgical technique is vital, however, to minimize the incidence of positive surgical margins and consequent recurrent disease. (Rosen M A et al., “Frequency and location of extracapsular extension and positive surgical margins in radical prostatectomy specimens,” J. Urol. 148:331, 1992).
Considerable interest has evolved in developing gene therapy vectors as therapeutic agents. Many proposed cancer therapeutic vectors are based on adenovirus. U.S. Pat. Nos. 5,631,236 and 6,096,718 (Baylor College of Medicine) cover a method of causing regression in a solid tumor, using a vector containing an HSV thymidine kinase (tk) gene, followed by administration of a prodrug such as ganciclovir. U.S. Pat. No. 6,096,718 (Baylor College of Medicine) relates to the use of a replication incompetent adenoviral vector, comprising an HSV tk gene under control of the alpha-lactalbumin promoter. U.S. Pat. Nos. 5,801,029 and 5,846,945 (Onyx Pharmaceuticals) relate to adenovirus in which the E1b gene has been altered so as not to bind and inactivate tumor suppressor p53 or RB proteins expressed by the host. This prevents the virus from inactivating tumor suppression in normal cells, which means the virus cannot replicate. However, the virus will replicate and lyse cells that have shut off p53 or RB expression through oncogenic transformation.
Adenoviruses are non-enveloped, regular icosohedral, double-stranded DNA viruses. The protein coat (capsid) is composed of 252 capsomeres of which 240 are hexons and 12 are pentons. Most of the detailed structural studies of the adenovirus polypeptides have been done for adenovirus types 2 and 5. The viral DNA is 23.85×106 daltons for adenovirus 2 and varies slightly in size depending on serotype. The DNA has inverted terminal repeats and the length of these varies with the serotype.
The replicative cycle is divided into early (E) and late (L) phases. The late phase defines the onset of viral DNA replication. Adenovirus structural proteins are generally synthesized during the late phase. Following adenovirus infection, host DNA and protein synthesis is inhibited in cells infected with most serotypes. The adenovirus lytic cycle with adenovirus 2 and adenovirus 5 is very efficient and results in approximately 10,000 virions per infected cell along with the synthesis of excess viral protein and DNA that is not incorporated into the virion. Early adenovirus transcription is a complicated sequence of interrelated biochemical events, but it entails essentially the synthesis of viral RNAs prior to the onset of viral DNA replication.
The organization of the adenovirus genome is similar in all of the adenovirus groups and specific functions are generally positioned at identical locations for each serotype studied. Early cytoplasmic messenger RNAs are complementary to four defined, noncontiguous regions on the viral DNA. These regions are designated (E1-E4). The early transcripts have been classified into an array of immediate early (E1a), delayed early (E1b, E2a, E2b, E3 and E4), and intermediate (IVa2.1X) regions.
The E1a region is involved in transcriptional transactivation of viral and cellular genes as well as transcriptional repression of other sequences. The E1a gene exerts an important control function on all of the other early adenovirus messenger RNAs. In normal tissues, in order to transcribe regions E1b, E2a, E2b, E3, or E4 efficiently, active E1a product is required. However, the E1a function may be bypassed. Cells may be manipulated to provide E1a-like functions or may naturally contain such functions. The virus may also be manipulated to bypass the functions.
The E1b region is required for the normal progression of viral events late in infection. The E1b product acts in the host nucleus. Mutants generated within the E1b sequences exhibit diminished late viral mRNA accumulation as well as impairment in the inhibition of host cellular transport normally observed late in adenovirus infection (Berkner, K. L., Biotechniques 6:616-629 (1988)). E1b is required for altering functions of the host cell such that processing and transport are shifted in favor of viral late gene products. These products then result in viral packaging and release of virions. E1b produces a 19 kD protein that prevents apoptosis. E1b also produces a 55 kD protein that binds to p53.
For a complete review on adenoviruses and their replication, see Horwitz, M. S., Virology 2d ed, Fields, B. N., eds., Raven Press Limited, New York (1990), Chapter 60, pp. 1679-1721.
Until relatively recently, the virtually exclusive focus in development of adenoviral vectors for gene therapy has been use of adenovirus merely as a vehicle for introducing the gene of interest, not as an effector in itself. Replication of adenovirus had previously been viewed as an undesirable result, largely due to the host immune response. More recently, however, the use of adenovirus vectors as effectors has been described (see e.g., International Patent Application Nos. PCT/US98/04084, PCT/US98/04080; PCT/US98/04133, PCT/US98/04132, PCT/US98/16312, PCT/US95/00845, PCT/US96/10838, PCT/EP98/07380, U.S. Pat. No. 5,998,205 and U.S. Pat. No. 5,698,443). The use of IRES in vectors have been described. See, for example, International Patent Application No. PCT/US98/03699 and International Patent Application No. PCT/EP98/07380. Adenovirus E1A and E1B genes are disclosed in Rao et al. (1992, Proc. Natl. Acad. Sci. USA vol. 89:7742-7746).
Publications describing various aspects of adenovirus biology and/or techniques relating to adenovirus include the following: PCT/US95/14461; Graham and Van de Eb (1973) Virology 52:456-467; Takiff et al. (1981) Lancet 2(8251):832-834; Berkner and Sharp (1983) Nucleic Acid Research 11 (17);6003-6020; Graham (1984) EMBO J 3:2917-2922; Bett et al. (1993) J. Virology 67:5911-5921; and Bett et al. (1994) Proc. Natl. Acad. Sci. USA 91:8802-8806. These references describe adenoviruses that have been genetically modified to produce replication-defective gene transfer vehicles. In such vehicles, the early adenovirus gene products E1A and E1B are deleted and provided in trans by the packaging cell line 293 developed by Frank Graham (Graham et al. (1987) J. Gen. Birol. 36:59-72 and Graham (1977) J. Genetic Virology 68:937-940). The gene to be transduced is commonly inserted into adenovirus in the deleted E1A and E1B region of the virus genome Bett et al. (1994), supra. Adenovirus vectors as vehicles for efficient transduction of genes have been described by Stratford-Perricaudet (1990) Human Gene Therapy 1:2-256; Rosenfeld (1991) Science 252:431-434; Wang et al. (1991) Adv. Exp. Med. Biol. 309:61-66; Jaffe et al. (1992) Nat Gen. 1:372-378; Quantin et al. (1992) Proc Natl. Acad. Sci. USA 89:2581-2584; Rosenfeld et al. (1992) Cell 68:143-155; Stratford-Perricaudet et al. (1992) J. Clin. Invest. 90:626-630; Le Gal La Salle et al. (1993) Science 259:988-990; Mastrangeli et al. (1993) J. Clin. Invest. 91:225-234; Ragot et al. (1993) Nature 361:647-650; Hayaski et al. (1994) J. Biol. Chem. 269:23872-23875.
There are several other experimental cancer therapies which utilize various aspects of adenovirus or adenovirus vectors. See, U.S. Pat. No. 5,776,743; U.S. Pat. No. 5,846,945; U.S. Pat. No. 5,801,029; PCT/US99/08592; U.S. Pat. No. 5,747,469; PCT/US98/03514; and PCT/US97/22036.
Of particular interest is the development of more specific, targeted forms of prostate cancer therapy. In contrast to conventional cancer therapies, which result in relatively non-specific and often serious toxicity, more specific treatment modalities attempt to inhibit or kill malignant cells selectively while leaving healthy cells intact. There is, therefore a serious need for developing specific, less toxic prostate cancer therapies.
Furthermore, an effective treatment for prostate cancer will kill both androgen-responsive and androgen-refractory cancer cells. Whereas commonly used androgen deprivation therapies induce apoptotic cell death in androgen-sensitive cells (Colombel, M. C., et al., Methods Cell. Biol., 46, 27-34, 1995; Buttyan, R., et al., In: Prostate—Basic and Clinical Aspects., pp 201-218, Naz R K (ed), CRC Press, Boca Raton, 1997; Perlman, H., et al., Cell Death Differentiation 6, 48-54, 1999; Bruckleimer, E. M., et al., Sem. Oncol., 26, 382-398, 1999), effective chemotherapy for androgen-refractory cancer is not available (Kozlowski, J., et al., Urol. Clin. N. Am., 18, 15-24, 1991; Santen, R. J., J. Clin. Endocrinol. Metab., 75, 685-689, 1992; Kreis, W., Cancer Invest., 13, 296-312, 1995). It would be advantageous to have means of inducing cell death in all prostate cancer cell types, including both androgen-sensitive and androgen-refractory prostate cancer cells.
All references cited herein are hereby incorporated by reference in their entirety.